The lanes reopened just before 9 a.m. on Tuesday.
OPP Sgt. Kerry Schmidt said the fatal crash happened just before 4 a.m. when an SUV rear ended into the back of a transport truck at around Dixie Road.
Schmidt said a female passenger of the SUV was pronounced dead at the scene while the male driver was taken to hospital with critical injuries.
The driver of the transport truck suffered no injuries, Schmidt said.
For a large part of the morning there was no access to the express lanes of the 401 from Highway 403. However, Highway 401 collector lanes were getting by as well as the westbound side of the highway was open.
There was heavy traffic volume as far back as Winston Churchill and beyond, Schmidt said.
Schmidt said the fatal collision was a secondary collision and occurred when traffic had slowed down due to a previous minor crash a few hundred yards away.
He also said there was at least one other secondary minor collision in the westbound lanes as cars slowed down to look.
“It is so critically important drivers that when you’re operating your vehicle you need to pay attention,” Schmidt said. “If there’s something happening in the peripheral adjust your driving accordingly but don’t focus your attention on that because if you’re looking somewhere else than where you’re going, we could see another repeat of this.”